Lighting panel for a display

ABSTRACT

A panel for lighting a display has a lighting panel made of a transparent plastic and having a rectangular shape in plan view. The lighting panel has a reflection surface and a discharge surface on opposite long sides and an incident surface on a short side of the lighting panel. A plurality of scalene prisms are formed on the reflection surface of the lighting panel. A flat plane is formed on the reflection surface, adjacent the incident surface. An equilateral prism is formed on the flat plane.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a lighting panel for a displaysuch as liquid crystal display (LCD) for illuminating the display fromthe underside thereof as a back light.

[0002]FIG. 10 is a perspective view showing a conventional lightingdevice, and FIG. 11 is a side view of the device.

[0003] A lighting panel 102 made of a transparent plastic has arectangular shape in plan view and has a discharge surface 102 a, areflection surface 102 b and an incident surface 102 c. Three edgelights 101 of an LED are mounted on a supporting plate 101 bcorresponding to the incident surface 102 c. On the reflection surface102 b, a plurality of prisms 102 b 1 are formed as reflector members.Each prism 102 b 1 comprise a first inclination side 102 b 11 oppositeto the incident surface 102 c and a second inclination side 102 b 12opposite to the first side.

[0004] The light emitted from the edge light 101 enters the lightingpanel 102. The light in the lighting panel 102 is reflected by theprisms 102 b and discharged from the discharge surface 102 a. Thedischarged light enters a prism sheet 103 and discharges from the prismsheet to be applied to an LCD 107.

[0005] Light discharged from the underside of the lighting panel 102 isreflected by a reflector sheet 106 to be returned to the lighting panel102.

[0006] Referring to FIG. 12, light emitted from the edge light 101enters the lighting panel 102 at an incident angle θi, and the lightproceeds in the panel 102 in a direction of θ in accordance with theSnell's law. There are following relationships between angle θi andangle θ.

θ=sin⁻¹((1/n)sin θi)   (1)

[0007] where n is the refractive index of the panel, and the refractiveindex of air is 1.

[0008] For example, if the refraction index n of the lighting panel 102is n=1.58 and θi=90°,

θ=sin⁻¹(1/1.58)=39.3°

[0009] Therefore, the critical angle θc is

θc=39.3°

[0010] The incident light is reflected by the discharge surface 102 a ata reflection angle θ1 which is larger than 50°. The reflected lightstrikes the second inclination side 102 b 12 having an inclination anglea at angle θ2=θ1−α, where α is between 1 degree and several degrees. Thelight is reflected by the second side 102 b 12 at the angle of θ2 andstrikes the discharge side 102 a at an incident angle θ3, θ3=θ2−α=θ1−2α.The light is reflected by the surface 102 a at the reflection angle θ3,and strikes the second side 102 b 12 at an incident angle θ4=θ3−α=θ1−3α.

[0011] Thus, the incident angle θ1 reduces α by α at every incidence,Namely in the case of N incidence times, the incident angle θN is

θN=θ1−Nα  (2)

[0012] When the incident angle θN becomes smaller than the criticalangle θc as follows

θN=θ1−Nα<θc   (3)

[0013] The light discharges from the discharge surface 102 a at anincident angle θ5. Consequently, the number of discharge light from anarea near the incident surface 102 c is small.

[0014] Furthermore, there is following described troubles in theconventional lighting panel.

[0015] Referring to FIG. 13, there appears bright lines 104 in a rangeS1 near the incident surface 102 c. In a range S2, lights are uniformlyand thickly discharged, hence there is no bright lines. The reason forthe generating of the bright lines will be described hereinafter.

[0016] Referring to FIG. 14, lights from the LED 101 striking a corner102 d of the:incident surface 102 c enter in the lighting panel 102 fromthe corner 102 d. The lights are diffused in the lighting panel. Lights21 of an incident angle θb smaller than the critical angle θc transmitsthe second inclination side 102 b 12 and is reflected by the reflectorsheet 106 and enters again in the lighting panel 102. The light s21transmits the lighting panel 102 and the prism sheet 103. Light s22 ofan incident angle θb larger than the critical angle θc is reflected bythe second inclination side 102 b 12 and transmits the lighting panel102 and prism sheet 103.

[0017] The number of incidences is determined before discharge of lightby the difference between the incident angle θb and the critical angleθc as described above. The number increases with the difference.

[0018] Referring to FIG. 15, φ1, φ2, φ3, φ4 are from the corner 102 d.Each of incident rays of light angles θd1, θd2, θd3 and θd4 of rays φ1,φ2, φ3 and φ4 is smaller than the inclination angle a of the secondinclination side 102 b 12. The relationship between the angles θd1, θd2,θd3, θd4 and the critical angle θc are as follows.

θd1=1.5α+θc

θd2=2.5α+θc

θd3=3.5α+θc

θd4=4.5α+θc   (4)

[0019] As shown in FIG. 15, the incident angles of the first incidenceto the second inclination side 102 b 12 areas follows.

θd1−α, θd2−α, θd3−α, θd4−α

[0020] These angles are larger than the critical angle θc as understoodfrom the formula (4). Consequently, all of the rays are reflected.

[0021] As the second incidence to the discharge surface 102 a, incidentangles are as follows.

θd1−2α<θc, θd2−2α>θc, θd3−2α>θc, θd4−α>θc

[0022] Only the rays φ1, the incident angle of which is smaller than thecritical angle θc, discharges from the discharge surface 102 a at awidth b1 of rays.

[0023] The reflection and discharge at third and fourth incidences areas shown in FIG. 15.

[0024] Widths of the rays increase with length of each ray in thelighting panel 102 as b1<b2<b3<b4, as shown in FIG. 15. Thus, the brightlines 104 generate as shown in FIG. 13. Such bright lines decrease thelighting effect for the LCD.

SUMMARY OF THE INVENTION

[0025] An object of the present invention is to provide a lighting panelwhich may prevent the generation of bright lines.

[0026] According to the present invention, there is provided a panel forlighting a display comprising a lighting panel made of a transparentplastic and having a rectangular shape in plan view, the lighting panelhaving a reflection surface and a discharge surface on opposite longsides, and an incident surface on a short side of the lighting panel, anedge light provided corresponding to the incident surface, a pluralityof scalene prisms formed on the reflection surface of the lightingpanel, a flat plane formed on the reflection surface in a range betweenthe incident surface and a group of the scalene prisms, and at least onefirst equilateral prism formed on the flat plane.

[0027] At least one second equilateral prism is formed on the dischargesurface adjacent the incident surface.

[0028] Each of the first and second equilateral prisms is formed into aform projected inside the panel.

[0029] These and other objects and features of the present inventionwill become more apparent from the following detailed description withreference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0030]FIG. 1 is a perspective view showing a 1 lighting device accordingto a first embodiment of the present invention;

[0031]FIG. 2 is a side view of the device;

[0032]FIG. 3 is a side view of a lighting panel;

[0033]FIG. 4a is an enlarged perspective view of a part A in FIG. 1;

[0034]FIG. 4b is a side view of an equilateral prism;

[0035]FIGS. 4c to 4 e are perspective views showing other examples ofthe prism;

[0036]FIG. 5 is an enlarged side view of the lighting panel;

[0037]FIG. 6 shows optical paths of rays from the lower corner D2;

[0038]FIG. 7 is a side view of a second embodiment of the presentinvention;

[0039]FIG. 8 is a side view of a third embodiment of the presentinvention;

[0040]FIG. 9 is a plan view of the lighting panel;

[0041]FIG. 10 is a perspective view showing a conventional lightingdevice;

[0042]FIG. 11 is a side view of the conventional lighting device;

[0043]FIG. 12 is a side view of a lighting panel;

[0044]FIG. 13 is a plan view of the device;

[0045]FIG. 14 is a side view of the device; and

[0046]FIG. 15 is a side view of a conventional lighting panel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0047]FIG. 1 is a perspective view showing a lighting device accordingto a first embodiment of the present invention, FIG. 2 is a side view ofthe device, and FIG. 3 is a side view of a lighting panel.

[0048] A lighting panel 2 made of a transparent plastic has arectangular shape in plan view and has a discharge surface 2 a, areflection surface 2 b and an incident surface 2 c. Three edge lights 1of LEDs are mounted on a supporting plate 1 b corresponding to theincident surface 2 c. On the reflection surface 2 b, a plurality scaleneprisms 2 bp are formed as reflector members. Each prism 2 bp comprises afirst inclination side 2 bp 1 opposite to the incident surface 2 c and asecond inclination side 2 bp 2 opposite to the first side. Theinclination angle a of the second inclination side 2 bp 2 is between 1degree and several degrees.

[0049] In accordance with the present invention, a flat plane 2 bhparallel to the discharge surface 2 a is formed on the reflectionsurface 2 b in a range adjacent to the incident surface 2 c. On the flatplane 2 bh, an equilateral prism 2 p is formed. Each of prisms 2 bp and2 p extends in the lateral direction of the lighting panel 2.

[0050]FIG. 4a is an enlarged perspective view of a part A in FIG. 1, andFIG. 4b is a side view of the equilateral prism 2 p. As shown in FIG.4b, the equilateral prism 2 p comprises a first inclination side 2 p 1opposite to the incident surface 2 c and a second inclination side 2 p 2opposite to the first inclination side 2 p 1, and the vertical angle θpis larger than 130°. In the case that the thickness of the lightingpanel 2 at the flat plane 2 bh is about 1 mm, it is desirable to providethe equilateral prism 2 p at a position in a range between 3 mm and 4 mmfrom the incident surface 2 c.

[0051] The light emitted from the edge light 1 enters the lighting panelat the incident surface 2 c. The light of a dotted line in the lightingpanel 2 shown in FIG. 2 is repeatedly reflected by the prisms 2 bp anddischarged from the discharge surface 2 a. The discharged light enters aprism sheet 3 and discharges from the prism sheet to be applied to anLCD 7.

[0052] As shown in FIG. 5, there is an upper corner D1 and a lowercorner D2 of the incident surface 2 c.

[0053] The lighting panel 2 is divided into four areas S1, S2, S3 and S4for light rays from the upper corner D1. The area S1 is an area betweenthe incident surface 2 c and the prism 2 p. In the area S1, the incidentangle of the incident light to the flat plane 2 bh is smaller than thecritical angle. Therefore, the light passes through the reflectionsurface 2 b, and is reflected by a reflection sheet 6 to be returned.The returned light passes through the lighting panel 2 and dischargesfrom the discharge surface 2 a as light s1.

[0054] In the area S2 which corresponds to the second inclination side 2p 2, the incident angle of the incident light is smaller than thecritical angle. Therefore, the light passes through the lighting panel2, and is reflected by the reflection sheet 6, and discharges as lights2. Since a plurality of light rays are continuously discharged, theredoes not appear bright lines in an area corresponding to the areas S1and S2.

[0055] In the area S3 corresponding to the first inclination side 2 p 1and the flat plane 2 bh on the right side of the prism 2 p, the incidentangle of the light to the first inclination side 2 p 1 is very largeTherefore, the reflected light discharges from the right end surface ofthe lighting panel 2 without discharging from the discharge surface 2 a,so that bright lines do not generate.

[0056] The incident angle of light s3 to flat plane 2 bh is very largeso that the incident angle is considerably larger than the criticalangle. Thus, the reflection is repeated large number of times (forexample 20 times) before the discharging of the light.

[0057] In the area S4, the light s4 is reflected on the secondinclination side 2 bp 2 because of a more larger incident angle. Thereflection is also repeated. As described above, the width of thedischarged rays increases with the length of rays in the lighting panel2. A large width of the discharged rays reduces the quantity of light inthe unit area, and hence reduces density of rays on the dischargesurface 2 a. Consequently, there does not appear bright lines.

[0058]FIG. 6 shows optical paths of rays from the lower corner D2. Lights5 discharges from the discharge surface 2 a because of a small incidentangle. The incident angle of light s6 is larger than the critical angle,so that the light is reflected four times before discharging. In such acase, there appears bright lines.

[0059]FIG. 7 is a side view of a second embodiment of the presentinvention. The second embodiment is provided for preventing thegeneration of bright lines caused by rays from the lower corner D2. Asshown in FIG. 7, an equilateral prism 3 p, which is shown in FIG. 4d,comprising first and second inclination sides 3 p 1, 3 p 2 is formed onthe discharge side 2 a at a position near the incident surface 2 c.

[0060] The light from the lower corner D2, which strikes an area on theleft side of the first inclination side 3 p 1, discharges from thedischarge surface 2 a because of a small incident angle, as light s7.

[0061] Next, the incident light to the first inclination side 3 p 1discharges from the side, since the incident angle thereof is smallbecause of the inclination of the side, as light s8. The incident angleof the light striking the second inclination side 3 p 2 is very large.Therefore, the light does not discharge from the discharge surface 2 a,as light s9. The light s10 striking the discharge surface 2 a repeatsreflection because of a large incident angle, thereby increasing thewidth of the discharged light. Consequently, bright lines do notgenerate. Thus, the light uniformly discharges from the dischargesurface 2 a as shown in FIG. 9.

[0062]FIG. 8 is a side view of a third embodiment of the presentinvention. There is formed two equilateral prisms 4 p on the dischargesurface 2 a, upwardly projected. The equilateral prism 4 p is shown inFIG. 4e. The light s11 striking the left side surface 2 a of theequilateral prism 4 p, discharges from the discharge surface 2 a becauseof a small incident angle.

[0063] The incident light s12 to the second inclination side 4 p 2 isreflected on the side on the first side 4 p 1 and on the reflectionsurface 2 b and discharges from the discharge surface 2 a. The incidentangle of the light s13 striking the first inclination side 4 p 1 issmall. Therefore, the light discharges from the discharge surface 2 a.Also light s14 discharges from the discharge surface 2 a. The light s15striking the discharge surface 2 a repeats reflection because of a largeincident angle, thereby increasing the width of the discharged light.Consequently, bright lines do not generate. Thus, the light uniformlydischarges from the discharge surface 2 a as shown in FIG. 9.

[0064] In accordance with the present invention, light lines can beprevented from appearing by the prism provided on a flat plane formedadjacent the incident surface of the lighting panel.

[0065] While the invention has been described in conjunction withpreferred specific embodiment thereof, it will be understood that thisdescription is intended to illustrate and not limit the scope of theinvention, which is defined by the following claims.

What is claimed is:
 1. A panel for lighting a display comprising: alighting panel made of a transparent plastic and having a rectangularshape in plan view; the lighting panel having a reflection surface and adischarge surface on opposite long sides and an incident surface on ashort side of the lighting panel; an edge light provided correspondingto the incident surface; a plurality of scalene prisms formed on thereflection surface of the lighting panel; a flat plane formed on thereflection surface in a range between the incident surface and a groupof the scalene prisms; and at least one first equilateral prism formedon the flat plane.
 2. The panel further comprising at least one secondequilateral prism formed on the discharge surface adjacent the incidentsurface.
 3. The panel according to claim 2 wherein each of the first andsecond equilateral prisms is formed into a form projected inside thepanel.
 4. The panel according to claim 2 wherein each of the first andsecond equilateral prisms is formed into a form outwardly projected fromthe panel.